1. Field of the Invention
The present invention relates in general to a method of forming an interconnection structure, and more particularly to a method of forming a multilayer interconnection structure.
2. Description of the Prior Art
With the progress of large-scale integration, requirements for an insulating film for planarization has become more strict. Hitherto, a spin-on glass (SOG) film has been used as an insulating film between aluminum conductive layers for the purpose of planarization. However, a SOG film has a very high moisture-absorbing characteristic as compared with other oxide films formed by chemical vapor deposition (CVD) method. Therefore, when a SOG film is exposed to the atmosphere, it adsorbs a large amount of moisture. If a cure after the SOG film coating is insufficient, water vapor is released from a SOG film upon heating after the cure. This tends to lower reliability of the device.
With reference to FIG. 9, a conventional method of forming a multilayer interconnection structure will be described.
Firstly, a first aluminum conductive layer 10 is formed on a substrate 12. Then, a first phosphorus-doped silicon dioxide (P--SiO.sub.2) layer 14, a SOG layer 16 and a second P--SiO.sub.2 layer 18 are formed in turn by the plasma CVD method on the first aluminum layer 10 so as to form a multilayer structure. Then, a through hole 20 is formed on the multilayer structure so as to expose an upper surface of the first aluminum layer 10. Then, the multilayer structure is heated for the purpose of the formation of a second aluminum conductive layer (not shown). However, as is shown by arrows of FIG. 9, water vapor is released into the through hole 20 from the SOG layer 16 by this heating. This water vapor oxidizes the exposed upper surface of the first aluminum layer 10, thereby forming thereon aluminum oxide. In the worst case, a void space is formed by the released water vapor in the through hole 20 after the through hole 20 is filled with the second aluminum layer. This leads to an insufficient ohmic contact between the first and second aluminum conductive layers.